1. Field of the Invention
The present invention relates to fuel vapor processing apparatus that can be installed on vehicles.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2008-202604 discloses a known fuel vapor processing apparatus. As shown in FIG. 10, the know fuel vapor processing apparatus disclosed in this publication includes a casing 120 with a tank port (charge port) 121, a purge port 122 and an atmospheric port 123. An inner space of the casing 120 is divided into a first adsorption material chamber 124 and a second adsorption material chamber 125 that communicate with each other via a communication passage 126. An adsorption material cartridge 132 is fitted into an end portion of the second adsorption material chamber 125 on the side of the atmospheric port 123. Activated carbon 131 is filled into the first adsorption material chamber 124 and the second adsorption material chamber 125 including the adsorption material cartridge 132. A non-filled space R having no adsorption material filled therein is defined between an outer peripheral surface of the adsorption material cartridge 132 and the inner peripheral surface of the casing 120 opposed thereto. The tank port 121 is connected to a fuel tank, the purge port 122 is connected to an intake manifold of an engine, and the atmospheric port 123 communicates with the atmosphere.
For example, when the engine is stopped, a fuel vapor containing air produced within the fuel tank is introduced into the casing 120 via the tank port 121, so that fuel vapor (HC gas) can be adsorbed by the activated carbon 131. After adsorption of the fuel vapor by the activated carbon 131, air is discharge into the atmosphere via the atmospheric port 123. During the operation of the engine, the fuel vapor adsorbed by the activated carbon 131 is desorbed and discharged to the intake side of the engine (i.e., the intake manifold) from the purge port 122. At the same time, air is introduced into the casing 120 via the atmospheric port 123. Exchanging the adsorption material cartridge 132 fitted into the end portion of the second adsorption chamber 125 on the side of the atmospheric port 123 to another cartridge can change an L/D ratio. Here, “L” designates a length of an activated carbon layer (adsorption material layer) within the adsorption material cartridge 132, and “D” designates a diameter (effective diameter) of a circular area that is equivalent to the cross sectional area of the activated carbon layer within the adsorption material cartridge 132.
The following is the reason as to why the L/D ratio is varied by exchanging the adsorption material cartridge 132 to another one. For example, if the L/D ratio is increased by varying the diameter D with the length L set to a fixed value, the resistance against flow of air may increase, while the residual amount of the fuel vapor after being purged may decrease, so that adsorption and adsorption abilities may be improved. On the other hand, if the L/D ratio is decreased, the resistance against flow of air may decrease, while the residual amount of the fuel vapor after being purged may increase, so that adsorption and adsorption abilities may be lowered. Therefore, it is necessary to set the L/D ratio to a value required for the fuel vapor processing apparatus 100, which value depends on the type of vehicle on which the apparatus 100 is installed. However, if different types of casings 120 are prepared for different uses, the manufacturing cost may increase. Therefore, different types of adsorption material cartridges are prepared for use in exchange for providing different L/D ratios, so that the casing 120 can be commonly used to save manufacturing cost.
According to the configuration of the known fuel vapor processing apparatus 100, although the activated carbon 131 is filled into the adsorption material cartridge 132, the non-filled space R having no adsorption material filled therein is defined between the outer peripheral surface of the adsorption material cartridge 132 and the inner peripheral surface of the casing 120. Therefore, a “blow-through” phenomenon may be caused to allow fuel vapor containing gas to be discharged to the atmosphere from the atmospheric port 123 though the non-filled space R without flowing through the activated carbon layer of the adsorption material cartridge 132. In order to prevent this “blow-through” phenomenon, a gasket 140 or the like is required between the second adsorption material chamber 125 of the casing 120 and the adsorption material cartridge 132 for sealing the non-filled space R. This leads to increase in the number of parts and the number of assembling steps of the apparatus, resulting in increase of manufacturing costs. In addition, a problem may exist that the gasket 140 or the like may be damaged or deformed during its assembling step or may be degraded during the long time use to cause leakage therefrom.
Therefore, there is a need in the art for fuel vapor processing apparatus that is designed for setting an L/D ratio and can prevent a “blow-through” phenomenon without need of a seal member.